Electric starter motors are widely utilized for cranking small gasoline engines such as those utilized in garden tractors, lawn mowers, snow blowers, outboard motors for boats, etc. In such a starter, a pinion drive provides the means for momentarily engaging the engine flywheel in transferring power from the electric starting motor to the internal combustion engine and then disengaging the starter motor from the flywheel once the engine has started to prevent damage to the starter motor. The most common way to facilitate engagement and disengagement of the pinion to the flywheel is to mount the pinion gear to a shaft so that it is rotatably driven by the motor and is axially movable along the shaft. The axial movement allows full engagement of the pinon gear with the flywheel during cranking and complete disengagement once the engine has started. The axial travel of the pinion gear is generally facilitated by one of two means. The pinion gear is either forced along the shaft by a solenoid or by inertia of the pinion gear interacting with the accelerating motor shaft by means of mating helical threads on the pinion gear and on the shaft. Exemplary starter assemblies are disclosed in Kern, U.S. Pat. No. 4,255,982 and McMillan, U.S. Pat. No. 3,690,188 which are incorporated herein by reference. In a typical configuration such as shown in U.S. Pat. No. 4,225,982, the flywheel of an internal combustion engine has gear teeth at its outer periphery and is juxtaposed with a spring biased pinion gear coupled to the output shaft of a starting motor through a torque-limiting friction clutch and a helical spline. When the starting motor is activated and begins to rotate, the inertia of the pinion gear resists rotation and the helical spline causes the pinion gear to translate axially along the starting motor shaft and into engagement with the gear teeth on the flywheel. The engine is thus cranked until the engine speed passes the speed at which it is driven by the starter motor whereupon the helical spline causes the pinion gear to disengage from the flywheel gear teeth. An anti-drift spring operates to urge the pinion gear toward the disengaged position.
As can be appreciated, a pinion drive assembly is subjected to high shock and loading stresses as it engages and disengages the engine flywheel. Such stresses are inherent as the motor armature and pinion are rotating as the pinion gear engages the large mass of the flywheel and engine components which are at rest. Also, once the engine is started, it begins to drive the starter assembly and the pinion gear is driven back along the shaft causing it to impact the armature shaft as it comes to rest against a stop. Consequently, a pinion drive assembly must be rugged overall and durable to withstand these high stresses and provide reliable operation.
In assembly, various methods have been utilized to retain the pinion drive assembly in place on the motor shaft. A typical configuration such as that shown in U.S. Pat. No. 3,690,188 utilizes a nut threaded to the terminal end of the motor shaft. Other types of retainers include a clutch retainer secured to the motor shaft by a spiral pin through a radial aperture in the motor shaft or a C-clip engaging a precision groove in the motor shaft. These types of securement exhibit shortcomings in terms of automated assembly and/or cost-effectiveness. For example, these retainers tend to be a relatively small-tolerance means of securement which increases cost. Further, the assembly steps which require radial or angular movement increases the relative complexity of automated assembly.
Accordingly, it is an object of the present invention to provide a new and improved engine starter apparatus and method of assembly which is highly automatable and cost-effective.
Another object of the invention is to provide a pinion drive assembly with a relatively high tolerance means of securement to a starting motor shaft.
A further object of the invention is to provide such a pinion drive assembly with a push-on means of securement which particularly facilitates automated assembly.
Another object of the invention is to provide an engine starter apparatus which is rugged, durable and reliable in use.
It has been found that the foregoing objectives are attained in an engine starter assembly which includes a starter motor having a rotatable shaft extending therefrom, a clutch subassembly slidably mounted on the shaft for frictionally coupling a pinion gear to the shaft, a pinion gear adapted for engaging and disengaging an engine drive gear and a drive retainer sleeve to retain the clutch subassembly on the shaft. The retainer sleeve is configured for push-on mounting over the terminal end portion of the motor shaft in snap lock engagement with the shaft to retain the clutch assembly on the shaft. The retainer sleeve includes a plurality of locking tabs configured for snap lock engagement with a circumferential groove on the motor shaft.
In the method of assembly, the clutch subassembly is positioned on the motor shaft adjacent the starter motor and the pinion gear is interconnected to the clutch assembly about the motor shaft. A clutch retainer sleeve is mounted to the shaft by axially pushing the retainer sleeve over the outer end of the motor shaft into snap lock engagement with the shaft to securely lock the clutch subassembly in place. The push-on mounting and locking action of the retainer sleeve is particularly adaptable to automated assembly.